The four Holy Roman Emperors named in the crossword are OTTO, Charles V, Francis I, and Joseph II. OTTO was the first of the four, reigning from 936 to 973. He was the founder of the Saxon dynasty and is often referred to as OTTO the Great. Charles V reigned from 1519 to 1556 and was the last of the four. He was a member of the Habsburg dynasty and was known for his extensive empire. Francis I reigned from 1745 to 1765 and was a member of the House of Bourbon. He was known for his reforms and his patronage of the arts. Joseph II reigned from 1765 to 1790 and was a member of the House of Habsburg. He was known for his enlightened absolutism and his attempts to reform the Austrian Empire.